Hirise Mars mission - full well, gamma?

I'm looking at what people write about the Mars caverns, and can't
make head or tail of what they say... E.g.:

What's amazing is that we cannot see any detail in the shadow

is "stretched" to best see the darkest area, yet we still cannot see
details except noise

(see http://hirise.lpl.arizona.edu/PSP_003647_1745, and the "stretched
version" in

http://hiroc.lpl.arizona.edu/images/2007/details/cut/PSP_3647_1745_cut_b.jpg)

Well, I can easily see the details in the dark area (there are 3
different levels of "gray" there), AND I do not see any noise to speak
off. It is clear that a lot of shadow details is cut out by
posterization (otherwise one would be able to see the noise).
However, without knowing more about the image (what is the gamma,
where was it converted to 8-bit - on-board vs on-the-ground, what is
the full well of the sensor in the mode the shot was made, what kind
of lookup tables they use) it is hard to make any deduction.

What I found is that the read noise is about 80 electrons, the
posterization is about 20 electrons/data-number, and that ADC has
about 13bits usable. I can guess that the maximum full well is about
128/8*26000 electrons. What about the rest?

Is it correct that there is practically no illumination from the
atmosphere diffuse lighting, and all the illumination of the bottom of
the cavern comes from stars (so it is the "night" illumination)? Then
what is the ratio of day/night illumination of the surface?

Thanks,
Ilya

 

Here's all I can get out of PSP32:

http://tinypic.com/view.php?pic=52xfl0w

No much in the way of detail, certainly nothing to be proud of or
useful!

 

[A complimentary Cc of this posting was sent to
DeanB

??? Did you see that there is no noise, and there are 3 levels of gray?

For me, this implies that there was a major posterization; AND this
posterization could not remove all details. My impression is that by
minor reprogramming, the shots can be repeated with a lot of details
in the darks. Is it so? And if it is, where are the shots?

Essentially, another of my questions is about calibration: one of
these 3 levels is "background" (read: black); now these 2 levels of gray
"above background", what is their actual brightness (in units of the
surface illumination, and in units of night illumination).

Thanks,
Ilya

 

To answer your questions, you might try reading the team's research
paper on the instrument, just published:

http://www.agu.org/pubs/crossref/2007/2005JE002605.shtml

Roger

 

[A complimentary Cc of this posting was sent to
Roger N. Clark (change username to rnclark)

It is not freely available. IAF_2004_Bergstrom_revH.pdf and 3287.pdf,
which I read before posting, does not contain the necessary info.

============================================

What else puzzles me, is the claim that "usually images of deep holes
on Mars contain details due to star illumination". On Earth, sunlit
is about 15ev, star illumination is about -6ev. On Mars, sunlit
should be about 14ev; even assuming that star illumination is 1 step
stronger (due to less atmospheric losses), this is 19 steps below the
sunlit part. As claimed, the imager's ADC has about 13 usable bits;
where the 6 other steps go?

Thanks,
Ilya

 

Gee, you can't afford $9?

That is strange.
If I get a chance, I'll ask Alfred, who I'll see in a couple of weeks
at a meeting.

Roger

 

[A complimentary Cc of this posting was sent to
Roger N. Clark (change username to rnclark)

Thanks,
Ilya